The invention relates to extreme pressure lubricating oils, particularly alkali metal borate-containing lubricants.
Alkali metal borates are well known in the lubricant industry for their usefulness as extreme pressure agents. See, for example, U.S. Pat. Nos. 3,313,727; 3,565,802; 3,819,521; 3,846,313; 3,853,772; 3,907,691; 3,912,639; 3,912,643; 3,912,644; 3,997,454; and 4,089,790.
U.S. Pat. No. 4,089,790 claims a synergistic lubricant mixture containing: (1) a hydrated potassium borate; (2) an antiwear agent selected from (a) zinc dihydrocarbyl dithiophosphate, (b) C.sub.1 -C.sub.20 ester, C.sub.1 to C.sub.20 amide or C.sub.1 to C.sub.20 amine salt of a dihydrocarbyl dithiophosphoric acid, (c) zinc alkyl aryl sulfonate, and (d) mixture thereof; and (3) oil soluble antioxidant organic sulfur compound.
U.S. Pat. No. 4,171,268 claims lubricant compositions containing a zirconium salt of a carboxylic acid and oil-soluble sulfur-containing extreme pressure agent.
It is one object of the invention to provide an alkali metal borate-containing lubricant which has superior load carrying properties.